The hydrogenase from Azotobacter vinelandii is being purified so that its properties can be compared with the hydrogenase recovered from soybean nodules. The hydrogenases recovered from blue-green algae also are being studied for their localization and for their properties. Verification is being sought for the claim that Shethna Fe protein II protects the nitrogenase of A. vinelandii against O2 inactivation. The examination of interactions among nitrogenase substrates and inhibitors is being completed.